Endemic freshwater demosponges in the littoral zone of Lake Baikal, Russia, dominate the benthic biomass, covering 44% of the benthos. We measured in situ sponge abundance and grazing and calculated sponge‐mediated fluxes of picoplankton (plankton <2 µm) for two common species, Baikalospongia intermedia and Baikalospongia bacillifera. By means of dual‐beam flow cytometry, we found retention efficiencies ranging from 58 to 99% for four types of picoplankton: heterotrophic bacteria, Synechococcus‐type cyanobacteria, autotrophic picoplankton with one chloroplast, and autotrophic picoplankton with two chloroplasts. By using a general model for organism‐mediated fluxes, we conservatively estimate that through active suspension feeding, sponges are a sink for 1.97 g C d−1 m−2, mostly from procaryotic cell types. Furthermore, grazing by these extensive sponge communities can create a layer of picoplankton‐depleted water overlying the benthic community in this unique lake.

This study compares carbon sequestration rates along two independent tidal mangrove creeks near Naples Bay in Southwest Florida, USA. One tidal creek is hydrologically disturbed due to upstream land use changes; the other is an undisturbed reference creek. Soil cores were collected in basin, fringe, and riverine hydrogeomorphic settings along each of the two tidal creeks and analyzed for bulk density, total organic carbon profiles, and sediment accretion. Radionuclides 137 Cs and 210 Pb were used to estimate recent sediment accretion and carbon sequestration rates.Carbon sequestration rates (mean˘standard error) for seven sites in the two tidal creeks on the Naples Bay (98˘12 g-C m´2¨year´1 (n = 18)) are lower than published global means for mangrove wetlands, but consistent with other estimates from the same region. Mean carbon sequestration rates in the reference riverine setting were highest (162˘5 g-C m´2¨year´1), followed by rates in the reference fringe and disturbed riverine settings (127˘6 and 125˘5 g-C m´2¨year´1, respectively). The disturbed fringe sequestered 73˘10 g-C m´2¨year´1, while rates within the basin settings were 50˘4 g-C m´2¨year´1 and 47˘4 g-C m´2¨year´1 for the reference and disturbed creeks, respectively. These data support our hypothesis that mangroves along a hydrologically disturbed tidal creek sequestered less carbon than did mangroves along an adjacent undisturbed reference creek.

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Mound Key was once the capital of the Calusa Kingdom, a large Pre-Hispanic polity that controlled much of southern Florida. Mound Key, like other archaeological sites along the southwest Gulf Coast, is a large expanse of shell and other anthropogenic sediments. The challenges that these sites pose are largely due to the size and areal extent of the deposits, some of which begin up to a meter below and exceed nine meters above modern sea levels. Additionally, the complex depositional sequences at these sites present difficulties in determining their chronology. Here, we examine the development of Mound Key as an anthropogenic island through systematic coring of the deposits, excavations, and intensive radiocarbon dating. The resulting data, which include the reversals of radiocarbon dates from cores and dates from mound-top features, lend insight into the temporality of site formation. We use these insights to discuss the nature and scale of human activities that worked to form this large island in the context of its dynamic, environmental setting. We present the case that deposits within Mound Key’s central area accumulated through complex processes that represent a diversity of human action including midden accumulation and the redeposition of older sediments as mound fill.

A biomechanical study of archaeocyathan (phylum Archaeocyatha) skeletal construction was undertaken in order to compare its function with that of poriferans. Flume experiments were conducted on three cylindrical, brass models of regular archaeocyathans. Two of these, the porous-septate and aporous-septate models (i.e., possessing septa either with or without pores), represent an ontogenetic series; regular archaeocyathans (class Regulares) typically exhibit a reduction in septal porosity as they grow and many have aporous septa as adults. The third model is aseptate and represents a morphology that is not found in the fossil record. All models exhibit passive entrainment of flow during flume testing, a phenomenon on which modern sponges depend for suspension feeding. Flow direction through the models is consistent with predictions of the spongiomorph-affinity hypothesis. The three models behave quite differently, however. The aseptate model is least effective at passive entrainment. Although some fluid exits the top of the central cavity (or osculum), a great deal of fluid is entrained out the top of the intervallum and also leaks out the outer wall. Flow induction from the oscula of the septate models is augmented when compared to the aseptate model. The porous-septate model exhibits slight leakage from the outer wall, and a dye-rich plume exits the top of the intervallum. Alternatively, the aporous-septate model exhibits no outer-wall leakage and no entrainment from the intervallum. These differences in flow pattern between the porous- and aporous-septate models suggest a hitherto unknown function for septa. Imperforate septa prohibit the migration of fluid through the intervallum to the low-pressure, downstream side where leakage occurs. The ontogenetic shift in septal porosity, common to many archaeocyathan species, may be a mechanism by which outer-wall leakage is avoided later in life. Archaeocyathans would have encountered progressively higher ambient current velocities as their height increased through growth. Outer-wall leakage is not a problem at low velocities or small sizes, but leakage becomes serious at higher velocities when tall, adult morphologies are attained.

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When assessing oyster-reef habitat in estuaries it is important to understand the influence of salinity on the spatial and temporal variability of associated organisms. How comparable is community structure among stations located at different points along the salinity gradients of estuaries or among tidal tributaries that experience different levels of freshwater inflow? Do assemblages vary seasonally in response to changing salinity and freshwater inflow? To address these questions, multivariate techniques were employed to analyze decapod crustacean and fish abundance data. Organisms were collected at three reefs along the salinity gradient of three estuaries: the Caloosahatchee River and estuary, Estero River and Bay, and Faka Union Canal and Bay. Additional collections were made from reefs located near the mouths of Estero Bay's five tidal tributaries. Samples were dominated by the decapods Eurypanopeus depressus and Petrolisthes armatus. Commonly occurring species included the decapods Panopeus obesus, Alpheus heterochaelis and Rhithropanopeus harrisii and the fishes Gobiosoma robustum, Lophogobius cyprinoides and Gobiesox strumosus. Analysis of similarities suggested differences among stations located along the salinity gradients of all three estuaries. Community structure also varied among stations located near the mouths of the tidal tributaries of Estero Bay. Multidimensional scaling identified community structure present at upper stations as distinct from that downstream and at high-flow tributaries as distinct from that near low-flow tributaries. Upper stations and stations near high-flow tributaries were typified by E. depressus and gobiid fishes. Downstream stations and stations near low-flow tributaries were typified by E. depressus and P. armatus. Percent dissimilarity was greatest when upper and lower stations were compared along the salinity gradient or when low salinity and high-salinity sites were compared among tributaries. Within-station sample variability tended to be higher upstream or in association with high-flow tributaries.

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